1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to image processing, and more particularly, to image processing for contrast enhancement.
2. Description of the Related Art
The real world has a wide, dynamic range of brightness. However, since display apparatuses for representing the real world have a limitation in the number of bits capable of being displayed, they may not represent the entire wide, dynamic range.
Also, when an image is obtained, if distortion is generated due to a conflict between the characteristics of several devices, the contrast of the image is reduced. In order to mitigate this problem, contrast enhancement (CE) is used.
Related art CE methods include histogram equalization (HE) and gamma correction. The HE method enhances a contrast using a probability density function (pdf) of an image as a mapping function, when an image having a low contrast exists due to an imbalance in a brightness distribution of pixels.
However, when the HE method is used, the effect or direction of lighting in an image can be cancelled or a false contour can be generated by sharply changing an area where pixels gradually change (for example, shadows). Also, if the CE method is performed only on a brightness Y, the corresponding original color can vary when the brightness Y is converted into a color.
The gamma correction method can enhance a contrast using a gamma function as a mapping function when an image having a low contrast exists due to an imbalance in a brightness distribution of pixels. However, when the CE method is performed based on gamma correction, it is difficult to set a gamma value suitable for each image, and an original color can change when a wrong gamma value is set.